This invention relates to paper handling devices, such as paper stackers, staplers, binders, and collators, which are used with printers and copiers and, more particularly, to holders for improving the quality of stacks of paper generated by such devices.
Dedicated printers, copiers and facsimile machines commonly employ paper handling devices which perform tasks such as stacking, stapling, binding and collating. Dual-purpose machines which incorporate both printing and copying functions are becoming increasingly common in the office environment. For home offices, multi-function machines which incorporate not only printing and copying functions, but facsimile send and receive functions as well, have become very popular.
Designers of paper handling devices coupled to printers and copiers must take into consideration the quality of paper stacks generated during an output session. At the very least, high quality stacks output bins are aesthetically pleasing. If the paper handling device is engaged in stapling and binding operations, stack quality cannot be ignored. Unevenly stacked paper sheets will neither bind nor staple well. In addition, it is far simpler to provide additional handling operations for neatly stacked sheets than for those which are stacked unevenly. For paper handling devices which generate an intermediate stack that is fed to another paper handling device, good stack quality eliminates the need to subject the stack to an extra registration process.
Poor stack quality may be caused by several factors. Some of those factors are:
(a) motion of a sheet of paper when a new job arrives on top of an existing stack of already printed sheets;
(b) misalignment of sheets in an existing stack brought about by vertical movement of an output tray as it returns to its home position;
(c) non planarity of individual sheets;
(d) non-transnational movement of individual sheets as they are ejected into the output tray;
(e) improper vertical positioning of the output tray as it begins to receive a new job;
(f) non-uniform size of print media sheets; and
(g) strain induced in sheets overlying one or more stacks of stapled sheets.
In studies performed at the printer development labs of the Hewlett-Packard Co., it has been ascertained that factor (a) is one of the most common causes of poor stack quality. What is needed is a mechanism for holding an existing stack of printed pages while the output tray repositions itself to receive a new job and while the new job is being output to the tray. The holding mechanism will prevent relative motion from arriving sheets pertaining to the new job from being transferred to the sheets of an existing stack.
This invention includes a weighted apparatus for gently holding an existing stack of paper at opposite sides thereof so that a new job may be deposited over the existing stack without degrading the stacking quality of the existing stack. The apparatus may be readily incorporated into many existing paper handling devices which have a paper output tray which is upwardly and downwardly movable in a vertical direction. The apparatus includes a mirror-image pair of paper hold mechanisms, each of which secures a single edge of the existing stack. Each mechanism includes an arm having a longitudinally-oriented slot in a laminar upper end portion thereof and a guide pin anchored to the frame of the paper handling device which passes through the slot. The arm is retained on the pin between a pair of flanged collets. The pin limits movement, which together, limit movement of the arm in a plane and. The collars limit movement of the arm within a plane, while the pin constrains the arm to movement along the length of the slot. The arm also incorporates both a cam follower attached to a center portion thereof, and a foot having a stack contacting roller at its lower end. The mechanism further includes incorporates a cam which is rigidly affixed to the frame of the paper handling device. As the output tray having an existing stack thereon rises upwardly against the roller-equipped feet and is brought to a vertical machine reference level, the arm slides upwardly over the guide pin. As a new output job is deposited on top of the feet, the output tray is lowered in order to maintain the reference level even with the top of the accumulating stack. Near the bottom of the tray""s travel, the arms swing outwardly, thereby disengaging the feet from both the existing stack and the newly deposited sheets. The arms are weighted so that each resets and holds both the existing stack and the newly deposited sheets as a single stack as the tray rises.
Two embodiments of cam and cam follower are disclosed. The first embodiment utilizes a cam having opposing faces first and second faces, each of which incorporates a path. The free end of the cam follower arm is positioned between both faces. A collar, which is rigidly affixed to the free end, encloses a follower pin that is laterally slidable between the two faces, so that the pin can engage a path on either face. The path on each face has a raised portion so that the follower pin can be transferred between the paths on the opposing faces. The second embodiment utilizes a cam having a single face and a topographic path. The lower portion of the upward vertical path is raised above the downward and outward curving path. A follower pin retainer is rigidly affixed to the free end of the cam follower arm. The retainer holds a spring-loaded laterally-slidable follower pin. Spring loading of the follower pin allows the pin to follow the topographic path. On the downward and outward curving path taken by the holder arm, the follower pin engages a low-level groove. However, on the lower portion of the upward vertical path, the path rises to a higher level. Thus, at the intersection of the rising vertical path and the downward and outward curing path, the follower pin abruptly drops off a high level ledge to the lower level. The follower pin continues to engage the lower level groove during the remainder of the upward travel. Other cam/cam follower systems that use separate downward and upward paths are also possible.